In the Wireless Relay technology in the Long Term Evolution-Advanced (LTE-A) standard issued by the 3rd Generation Partnership Project (3GPP) standard organization, a Relay Node (RN) provides to a User Equipment (UE) accessing a cell of the relay node functions and services which are similar to those of a common evolved Node B (eNB), and then accesses an eNB (called a Donor eNB (DeNB)) serving the relay node via a wireless interface in a manner similar to a common UE. As the high speed railway is massively constructed and put into operation, the demand for communications on the train is increasing constantly. However, since the high-speed moving train is influenced by Doppler frequency shift, cell frequent handover and great penetration loss of high-speed rail carriage and so on, coverage of the existing network base stations is hard to meet communication quality requirements of the high-speed rail. Therefore, the industry proposes to deploy a relay node on the high-speed rail, and this relay node is generally called as a Mobile Relay Node (MRN). As shown in FIG. 1 and FIG. 2, by the mobile relay technology, users (a UE1 and a UE2) on the high-speed rail train can communicate with a relatively resting MRN, and the MRN can be switched among various DeNBs in the process of the high-speed rail moving, thereby avoiding simultaneous handover of a large number of users in the high-speed rail carriage and guaranteeing the communication quality between the UE and the MRN. Moreover, a series of problems existing on the high-speed rail can be better solved by enhancing a backbone connection between the MRN and the DeNB.
A mobile relay system can adopt an architecture shown in FIG. 1 (i.e., an architecture which is the same as the standardized R10 fix relay and generally called as architecture 2). In this architecture, a Service Gateway (S-GW), a Packet Data Network Gateway (P-GW) and a relay Gateway (relay GW) which serve the MRN are built in the DeNB, wherein the relay GW in the DeNB provides S1 and/or X2 agent functions for user plane data and control plane signaling of the UE. In this architecture, the S-GW, P-GW and relay GW (collectively called as GW) of the MRN are located in an initial DeNB which is assessed by the MRN when the MRN attaching. When the MRN on the high-speed rail moves far away from the initial DeNB, after the data of the UE reach the P-GW of the MRN, the data of the UE can reach the DeNB serving the MRN through forwarding and routing of multiple DeNBs, that is, there exists a problem that the routing path is too long, thereby causing delay increase of the data of the UE. Therefore, a routing optimization scheme can be considered, for example, when the MRN moves far away from the initial DeNB, during handover of the MRN the GW of the MRN is changed to be the built-in gateway in a DeNB which serves the MRN. As shown in FIG. 2, before the handover of the MRN, the GW of the MRN is located on DeNB1, and when a base station function of DeNB3 provides services for the MRN, the data of the UE firstly reach the GW function of the DeNB1, and then route to the base station function of the DeNB3 via DeNB2; the MRN can relocate its GW to the GW built in DeNB4 in the handover process, so that the data of the UE can directly reach the GW in the DeNB4, which shortens the path length and reduces the data delay. Since it is not required to execute the gateway relocation in each handover of the MRN, it is only required when the routing path is comparatively long. Moreover, in the architecture 2, due to the S1 and X2 agent functions of the DeNB, a target DeNB is required to meet a certain condition, and the gateway of the MRN can be relocated to the S-GW and P-GW built in the target DeNB. In a word, it is required to solve a problem of how to judge whether to execute the gateway relocation in the process of the current handover of the MRN.
The mobile relay system also can use an architecture shown in FIG. 3 (generally called as an architecture 1), there is no relay GW function entity in this architecture, the S-GW and P-GW providing services for the MRN are located in a core network, the DeNB encapsulates the user plane data and control plane signaling of the UE into a General Packet Radio Service (GPRS) Tunneling Protocol for Userplane (GTP-U) data packet and sends to the S-GW and P-GW of the MRN through a bearer of the mobile relay, and then routes the GTP-U data packet to an MME or S-GW of the UE through an Internet Protocol (IP). With the high-speed movement of the train, when the GW serving the MRN and located in the core network is far away from the MRN, there also exists the above problem that the routing path is too long. It can also consider to relocate the GW of the MRN to an S-GW and P-GW close to a DeNB serving the MRN currently in the process of the handover of the MRN. Similar to the description in the architecture 2, it is also required to solve the problem of how to judge whether to execute the gateway relocation in the process of the current handover of the MRN.